The invention relates to a method and an arrangement for checking the operability of a vessel, especially a tank-venting system of a motor vehicle including a tank and an adsorption filter. The adsorption filter is connected to the tank via a connecting line and has a venting line as well as a pressure source connected forward of the venting line.
In various areas of technology, vessels must be checked as to operability, that is, as to tightness. Accordingly, for example, in chemical processing technology, it is important to check the tightness of vessels. Furthermore, it is also necessary in the area of motor vehicles to check the tightness of tank systems.
In this context, reference is made to more rigorous statutory requirements for the operation of internal combustion engines which are being sought in several countries, such as in the United States, by the governments thereof. In accordance with these requirements, it is, for example, necessary that motor vehicles, which utilize volatile fuels such as gasoline, have a control device as mentioned initially herein which can also find an existing leak in the tank or in the entire fuel tank system.
A method and an arrangement for checking the operability of a tank-venting system of a motor vehicle is disclosed, for example, in U.S. Pat. Nos. 5,349,935; 5,890,474; 6,131,550; and, 5,898,103. In these methods and arrangements, an overpressure is introduced into the tank-venting system and a conclusion is drawn as to the presence of a leak from an evaluation of the pressure trace.
Japanese patent publication 6-173837 and U.S. Pat. No. 5,347,971 disclose methods for checking the operability of a tank-venting system wherein a reference leak is switched into the tank-venting system and wherein a statement as to the presence of a leak is made from a comparison of the measurements with and without the reference leak.
In addition, it is known from U.S. Pat. No. 5,890,474 that a backpressure is formed between a pump and a reference leak whereby the pump rpm is lowered and the flow capacity of the pump is increased. The steady-state flow, which adjusts, is stored and, thereafter, the pumped air flow of the pump is pumped via a switchover valve past a reference leak into the tank. If the tank is tight, then a higher pressure builds up than when pumping against the reference leak. The flow capacity of the pump is therefore higher. For a leak less than the reference leak, the pressure which adjusts lies below the reference pressure and the flow capacity is therefore less.
When there is a leak present in the tank system, it can happen in these methods and arrangements during the diagnostic procedure that slight quantities of the hydrocarbon-containing vapors are outputted to the environment via the leak because of the generated overpressure. Measurements and computations have shown that these quantities can be neglected even when applying the strongest emission standards. The foregoing notwithstanding, it would be more advantageous when even the above-mentioned slight emissions would not occur.
In view of the above, it is an object of the invention to provide a method and an arrangement of the kind described above which are so improved that the above-mentioned slight emissions are completely avoided.
It is intended that, with the method and arrangement mentioned initially herein, the smallest possible amounts of toxic substances reach the environment during a function or tightness test of the vessel.
The method of the invention is for checking the operability of a vessel having a venting line. The method includes the steps of: providing a pressure source and connecting the pressure source to the venting line; generating an underpressure in the vessel and obtaining at least one of:
(a) a pressure trace of the pressure in the vessel; and,
(b) a volume flow moved by the pressure source; and, drawing a conclusion as to the presence of a leak in the vessel from at least one of the pressure trace and the volume flow.
A special characteristic of the method of the invention is that an underpressure is generated in the vessel and a conclusion is drawn as to the presence of a leak from the pressure trace and/or the pumped volume flow. The underpressure is generated by means of a pressure source through the adsorption filter. Compared to the known methods, no air is pumped into the vessel because of a reversal of the pumping direction; instead, the occurring gases or vapors are drawn by suction from the vessel. With the suggested underpressure method, increased hydrocarbon emissions because of the presence of a possibly present leak are effectively avoided. Especially the gases and vapors, which are drawn in by suction by the pressure source, are completely liberated from hydrocarbon substances because of the active charcoal filter connected between the vessel and the pressure source. Accordingly, these gases and vapors can then be outputted to the environment without problems for the environment.
Preferably, it is provided in the method of the invention that the vessel and a reference leak, which is connected in parallel to the vessel, are alternately charged with underpressure. The pressure trace or the volume flow pumped by the pressure source is detected during the underpressure in the vessel as well as during the underpressure at the reference leak. Then, a comparison is made of the pressure traces or volume flows and a conclusion is drawn therefrom as to the presence of leak. In this way, a more precise statement with respect to the presence of a leak can be made. The air flow, which is inducted from the reference leak, is already free of toxic substances and can therefore be outputted to the environment without problems for the environment.
In one embodiment of the method of the invention, it is provided that at least one operating characteristic variable of the pressure source is detected when generating the underpressure for determining the pressure trace and/or the pumped volume flow. From the above, a conclusion is drawn as to the presence of a leak. This makes possible an especially simple detection of the quantities required for the determination of the leak.
It can be especially provided that at least one of the following can be used as operating characteristic variable(s): the current drawn by the pressure source, the electric voltage applied to the pressure source and the rpm of the pressure source.
The pumped flow of the pressure source can be guided into an intake system of the engine of the vehicle in order to even more effectively avoid the output of toxic substances to the ambient.
In the arrangement of the invention, it is especially provided that the pumping device of the pressure source is so adjusted that an underpressure is generated in the vessel by means of the pressure source and that an electric circuit unit is provided for detecting and evaluating at least one operating characteristic variable of the pressure source during the underpressure in the vessel.
Preferably, the arrangement includes a reference leak arranged parallel to the vessel and the reference leak can be connected alternatively to the vessel and the pressure source via a switching device such as a switching valve.
In one embodiment, it is provided that the pumping output of the pressure source can be connected to the intake system of an engine of the vehicle via a return line.
The pressure source itself is preferably realized as a pump such as a vane-cell pump.